Biological samples can be stimulated by light energy. Stimulation can initiate, enhance, and/or inhibit one or more activities performed by a portion of the biological sample stimulated by the light energy. In some cases, nerve cells can be activated or deactivated by light energy. One or more populations of nerve cells can communicate signals based on activation by light energy. Biological samples can have small spatial scales such that they may comprise one or more features, such as cells, that are not visible to a human eye. Microscopes can be employed to visualize the small features of biological samples.